Dynamic assimilation and leaf gas exchange survey measurements

Link To Share This Poster: https://cdmcd.co/Rrm98J
Live Discussion Link: https://cdmcd.co/MpQ3Ma

Cici Hall, Douglas J. Lynch and Aaron J. Saathoff, LI-COR Biosciences, Lincoln, NE, Aaron J. Saathoff, Dept. of Natural Resources, University of Nebraska-Lincoln, Lincoln, NE

Background/Question/Methods
Survey measurements are a widely used gas exchange technique that allows researchers to quickly obtain real-time information of leaf physiological parameters such as assimilation (A), transpiration (E), and stomatal conductance (gsw). Gas exchange survey measurements generally take 1-2 minutes per leaf or measurement. This time requirement is mainly due to the steady-state premise of traditional gas exchange measurements which requires stable leaf chamber conditions for measurement accuracy. Obtaining chamber stability is, in turn, a function of flow rate, chamber volume, leaf biology, and environmental control system capabilities. Here, we present a new approach termed the Dynamic Assimilation Technique (DAT) that does not require steady-state conditions for measurement. DAT was implemented using the LI-6800 Portable Photosynthesis System and then assessed to see if performance gains were possible for gas-exchange survey measurements. We compared DAT and steady state measurements with the goal of reducing survey measurement time requirements. An artificial leaf with a semi-permeable membrane was used to provide a flux of CO2 and water vapor into the leaf chamber. Results from the artificial leaf were also compared to those obtained from a live leaf.
Results/Conclusions
The results showed that the artificial leaf was able to provide a constant CO2 flux into the leaf chamber of around 27 μmol m-2 s-1 and a constant water vapor flux of around 3-5 mmol m-2 s-1 into the leaf chamber. Furthermore, dynamic assimilation reached a stable value for A and E in around 15 s, which was substantially faster than measurements based on steady state principles which typically required an additional 15-30 s. These results were confirmed using live leaves; taken together, the data suggested that DAT should result in time savings for each survey measurement and thereby allow for higher overall survey measurement throughput.